Question

If it takes 10 people 6 days to do a home improvement, how long would 4 take

Answer 1

60 person days/job

(1/60) job/person day

(1/60)job/person day *(4) persons = 4/60 job/day = 1/15 job/day
so
15 days

Answer 2

4/10 as many people means 10/4 as long to work.

5/2 * 6 = 15